Apparatus for manufacturing wound grid electrodes



Sept. 18, 1934. MURPHY. 1,974,312

APPARATUS FOR MANUFACTURING WOUND GRID ELECTRODES Original Filed Sept. 25,1928

Inventor George F. Muu phg,

Attorney.

Patented Sept. 18, 1934 APPARATUS FOR PATENT- OFFICE GRID ELECTRODES George F. Murphy, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Original application September 25. 1928, Serial No. 308,293. Divided and this application Octobel. 19, .1933, Serial No. 694,217 I r 3 Claims. (01. 140-71) The present invention relates to grid electrodes for electron discharge tubes and more particularly to tools and devices for assembling and manufacturing the grid. This application is a 5. division of my prior application Serial No. 308,293,

filed September 25, 1928, and entitled Grid electrodes.

Patent No. 1,432,411- granted October 17, 1922 to J. H. Payne, Jr. discloses a helical grid structure comprising a large number of turns of wire of relatively small diameter which are self supporting and which require-no weldedjoints between the various elements for maintaining them in their proper spaced relation. The structure employs a number of small helices whichserve to space the grid turns, the helices being locked in position by means of stay rods which extend longitudinally through each of the helices and force certain turns of the latter against the larger grid wires.

The present invention contemplates improvements over the type of grid disclosed insaid patent in that the grid wires are more securely fixed at the proper spacing to the grid stays and in that economies are effected in grid material and also in the time necessary formanufacture. In

' brief, these ends are'attained by providing coils ,of relatively heavy, self-supporting wire in place of the small helices of fine wire disclosed in the a Payne patent, said coils being bent to such a shape, which broadly may be termed elliptical,

so as to conform closely to a. relatively large portion of the superficial surface of the mass of metal forming the junction at the places of con-- tact between the stay wires and the grid helix. The extent of the portion of metal over which,

the coil bears is considerably greater than in the case of the Payne helices which are strictly circular in shape and which bear merely along a 40 line contact; the coil which constitutes a feature of the present'invention is in a position to firmly clamp and rigidly hold the junction between the stay wires and the grid helix. My

- objects of the invention are to provide a novel form of grid which is of simpleconstruction; to provide a rigid attachment between the grid wires and stays without the use of welded joints; to

employ in the manufacture of the grid, the minimum amount of material'andlabor; to provide a grid structure having improved operating characteristics and a long operating life. The object of the invention claimed in the present divisional application is to provide improved devices for assembling and manufacturing the improved grid. In particular, the present invention contemplates the use of a collapsible mandrel on which the grid may be quickly and uniformly fabricated, also spacer members for holding the grid intact during the necessary heat treatments. Other objects and features will be apparent as tlfe'specification is perused in connection with the accompanying drawing in which similar reference characters designate corresponding elements through the several views. As an example of another feature, the present invention contem plates the use of a collapsible mandrel on which ,the grid 'may be quickly and uniformly fabricated. 'Fig. 1 shows in perspective, a view of the improved grid; Fig. 2 illustrates a portion of the mandrel employed in the manufacture of. the

grid; Fig. 3 is a plan in detail of the lower part of the mandrel; Fig. 4 shows a blank upon which the binding coils conveniently may be formed; Fig. 5 is an assembly view of the complete mandrel and a partially complete grid assembled on the mandrel; Fig. 6 is a perspective view showing the spatial relation between the component parts of the grid structure; Fig. '7 is a view, in perspective, of the combined grid and spacer members preparatory to firing. I

The grid structure shown in Fig. 1, as made in accordance with the present invention, comprises a helical 'member 1 of refractory metal such as tungsten, wound in the manner to be described, upon longitudinally-extending stay wires 2, also preferably of tungsten and secured thereto in proper spaced relation by means of several coils of wire arranged parallel to the stay wires. coils tightly embrace the helix and stay wires at each place of contact so that there is positively no relative movement between these members. The grid proper is terminated at each end by a ring member 4 which may be made of molyb denum, ears 5 being formed on each ring member having apertures through which the stay wires may be threaded. The grid may be supported from the stem of the tube by means of four equidistantly spaced rods fi which are, afiixed to the lower ring, preferably by welding; the other ends of these rods are secured to an ordinary form of clamp '7 provided with screw-bolts for tightly em bracing the stem of a tube in the well-known manner. Intermediate the lower ring 4 and the clamp 7, there is'positioned a ring member 8 The which fits about the rods 6 in the manner shown to lend rigidity to these rods and to maintain the spacing thereof. The grid proper is formed preferably on a collapsible mandrel, shown more clearly in Figs. 2 and 3. The mandrel is made up of a tapered, centrally disposed rod 9, the end with the larger diameter fitting into a collar 10 having suitable bore and the end of smaller diameter fitting within the space formed by a plurality of equidistantly spaced 'pins' 11 which extend radially from the interior surface of a collar 12 as seen more clearly in Fig. 3. About the tapered rod, there are a plurality of segmental members or sectors (six as illustrated) of a number corresponding to the number of spaces between the pins 11 on the collar 12. These seg= ments are provided at each end with extensions 14, 14 and are hollowed out along the inner surface to conform to the periphery of the rod 9; the outer surfaces of the extensions fit snugly within the respective collars. Each segment contains a longitudinally-extending, rectangularly-- shaped slot 15, the purpom oi which will be set forth hereinafter and also a series of transverse collar 12, also between each pair of adjacent pins 11-11. The upper collar is then placed in position to embrace the outer diameter of the upper extensions 14 which when assembled present a cylindrical surface. The mandrel is rendered tight and rigid by tapping the rod 9 at the larger end which serves the more securely to clamp and wedge the members 14 against the restraining collars 10 and 12.

After the mandrel has been assembled, the grid helix 1, which has been fabricated elsewhere, is then positioned in the threads 16 formed in the sectors 13; this may be conveniently accomplished by rotating the mandrel and holding the helix stationary until the first thread catches with the first turn of the helix after which rotation of either the mandrel or the helix will serve to completely thread the latter about the mandrel. The next step is that of forming the binding coil, which may be wound on a bar or rod 17, substantially rectangular in cross-section, .as shown more clearly in Fig. 4, the bar preferably being rotated between centers and the wire applied by a carriage which moves the length of the bar, screwthread fashion to maintain proper tension and to give a uniform pitch to the wire. It is evident that the shape and dimensions of the bar 1'7, also the gage and pitch of the wire member 3 are dependent upon many factors, including the gage of the grid and stay wires, also the pitch of the grid, and must be determined experimentally for each size of grid. In making the determinations, it is to be borne in mind that the shape of the recurring loops and their distance apart must be such that the wire snugly embraces and securely binds the stay-wires to the helical grid at the places of contact. It is obvious that the shape of each loop cannot be circular because, in height, the loop must embrace the stay-wire and grid helix along the combined diameters whereas in width the loop need extend over only one of the grid turns, making for a rectangularly-shaped -mea.ns of straps 19 formed of loop having height substantially twice as great as width. However, on account of limitations of pliability in the wire, these loops take on a shape which may be characterized as a series of bends and straight portions and in general, elliptical, as

by curved surfaces which constituted the original periphery of the round stock. Ihe pitch of the wire along the bar obviously corresponds to that of the grid helix and sufficient tension must be applied to conform the wire as fanas possible to the surface of thebar. The next step in the manufacture of the grid is to insert a looped member 3 or coil along each of the slots 15, if nec essary, tainping or pressing the loops over the grid wires. The stay wires are. then introduced one at a time from one end of the mandrel, these wires serving as a wedge between the lower loop portion of the coils 3 and the under surface of each grid turn at the place of contact, as indicated more clearly in Figs. 5 and 6. When the coil member has been properly designed including the shape and distance apart of the loops, a slight pressure exerted longitudinally of the stay wires is necessary to force same into position at whiclr time the various members are rigidly locked into the proper spatial relation. It is evident that the transverse threads on the mandrel preclude any relative movement between the turns of the grid during this operation. Moreover, the longitudinal slots in the mandrel positively position the looped members and stay wires so that strict uniformity of grid construction is assured. The stay wires may then be cut so that there is a sufficient length extending beyond each end .of the mandrel to accommodate the ring shaped members 4, 4 after which the wires are pointed in the manner shown in Fig. '7, to facilitate threading through the apertures in the ears 5 of said members. The surplus material may also be removed from the looped members 3, the ends being secured to the stay wires in any suitable manner, for example, by twisting or otherwise securing a full turn about each stay wire. In practice, it may be desirable to provide at the outset, stay wires of the proper length and suitably pointed to obviate the step of cutting and pointing these wires at this time. After rings 5, 5 have been afllxed on the stay wires,

the projecting ends of the latter are nipped off tortion in shape during the firing process described hereinafter. These spacers may take the form of bars of rectangular cross-section and of suitable length, having a series of transverse grooves which match the grid turns and serve to maintain the spatial relation between the said turns when the mandrel is disassembled. As shown in Fig. 7, three such spacers are usually sufllcient, the spacers being arranged about the grid, intermediate several pairs of stay-wires, by

wire.

twisted lengths of The next step'is to remove the mandrel from the grid and this is readily dpne by tapping the tapered rod 9 at the smaller end, withdrawing disengage.

same. .to allow sectors 13 and collars 10 and 12 to The next step in the fabrication of the grid proper is the firing process in which the grid and spacer members combined are subjected v allowed a certain amount of elongation of the grid under the heated conditions because the Joints are not rigidly fixed in a manner such that welded joints would produce. The spacer members serve to prevent any serious distortion of the wire framework under these conditions.

Upon cooling the structure, the welds between the stay wires and both rings may be made, preferably in a hydrogen atmosphere, with the spacers in place. the welds serving to rigidly fix I the rings in their proper linear positions along the stay wires. The spacer members may then be 'removed by untwisting the wire bands 19. The ends of the grid helix may be secured to the respective ring members by means of metallic tabs (not shown) which embrace the rings, and have extensions to which the ends of the grid helix may be welded'or otherwise attached. The final steps are those of aflixing the support rods 6 to the lower ring member '5 by arc welding and the treatment of the grid in a sand blast'to reduce the possibility of secondary emission from the various surfaces.

A grid made in the manner described is char acterized by a number of features, among which are: lack of resiliency or relative movement be-, tween the various turns nothwithstanding the total absence of welds at theplaces ofcontact between the various grid turns and stay wires; simplicity of manufacture; a high degree of reproducibility and utilization of the minimum amount of material which is advantageous from several staridpoints including that of less cost, particularly in view of the expensiveness of tungsten, also that of facilitating the denudation of the material of the gas held in occlusion, also from the standpoint of providing substantial uniformity of material at successive points about the' periphery of the grid which imparts to the latter a good operating characteristic. The rigidity of the various turns is derived from the peculiar formation of the binding coils which are con- 3 structed to tightly grip the large new: and the stay wires over a large surface. positively precluding the slightest movement therebetweem It will be evident that'in departing from a circular or true helix, the shape of the loops is such that the stress exerted thereon is mostly in the nature ,of. a longitudinal pull rather than torsional and hence, advantage is taken of the greater resisting power offered by the metal to longitudinal strain. This type of grid'also lends itself readily.

to construction on a mandrel which facilitates manufacture and uniformity of reproduction.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A collapsible mandrel for fabricating helical grids comprising a plurality of sector members of a length comparable to the length of the grid and arranged about a -tapered rod, said members having a series of transverse grooves which form, when the mandrel is assembled, a thread of substantially the same pltclg-and diameter as the helix, each of said members being also provided with'a longitudinally extending slot adapted to receive a grid stay-rod and binding wire, and means for clamping the sectors in place about the taper d rod. a

2. A collapsible mandrel for fabricating helical grids comprising a pluralityof sectormembers of a length comparable to the lengthof the grid, and arranged about a tapered rod, said members having a series of transverse grooves which form, when the mandrel is assembled, a thread of sub-' stantially' the same pitch and diameter as the helix,each of said members being also provided with'a longitudinally extending slot adapted to 11() receive a grid stay-rod and binding wire, and means comprising annular members which fit over predetermined portions of said sector members for clamping the sectors in place about the tapered rod.

3. Apparatus for the manufacture of helical grids for electron discharge devices, said apparatus including a plurality of spacer members comprising metal bars, said bars being spaced longitudinally abouta helical grid and rigidly held in place, the convolutions of the grid being secured to stay rods, each of said bars having a series of parallel-transversegrooves spaced apart distances corresponding to the pitch of the grid,

and said grid fitting within said grooves, whereby the convolutions of the grid are maintained in a fixed spaced relation during manufacture of the grid. I

- GEORGE F. MURPHY.

its 

